Increased Risk of Periprosthetic Femoral Fracture with Cementless Collared Metadiaphyseal-Filling Stems Compared to Cemented Fixation for Femoral Neck Fractures in Patients Aged 65 Years or Older: An American Joint Replacement Registry Analysis.

INTRODUCTION: Cemented femoral fixation is recommended when treating a femoral neck fracture with arthroplasty. Prior studies have shown collared, metadiaphyseal-filling (CMDF) cementless stems to have an equivalent periprosthetic fracture risk compared to cemented stems in primary total hip arthroplasty (THA). This study assessed the associated risk of periprosthetic femoral fracture (PPFx) after hemiarthroplasty or THA for femoral neck fracture comparing CMDF stems to cemented stems utilizing the American Joint Replacement Registry (AJRR). METHODS: All femoral neck fractures in patients aged ≥ 65 years treated with arthroplasty in the AJRR were linked to Centers for Medicare and Medicaid Services data from 2012 to 2022. Patients were included if they received a cementless CMDF stem or a cemented stem. Patient demographics, revision or open reduction and internal fixation (ORIF) for PPFx, and revision for aseptic loosening or dislocation were recorded. Cause-specific Cox proportional hazard models, were used to evaluate the association of stem design with all-cause revision, revision or ORIF due to PPFx, and revision for aseptic loosening or dislocation while adjusting for potential confounders. RESULTS: Compared to cemented stems, cementless CMDF stems were associated with a higher hazard of revision for PPFx (aHR [adjusted hazard ratio] 1.7, 95% CI [confidence interval] 1.1 to 2.7, P = 0.02). Analysis of secondary outcomes indicated that the two groups significantly differed in terms of revision for aseptic loosening, with cementless CMDF stems indicating a much lower event rate than cemented stems (aHR 0.5, 95% CI 0.2 to 0.9, P = 0.04). There were no significant differences found on adjusted analyses of other secondary outcomes. CONCLUSIONS: Cementless CMDF stems were associated with an increased risk of revision for PPFx in the treatment of femoral neck fractures when compared to cemented stems. While this finding supports the use of cemented stems for the treatment of femoral neck fractures, it should be assessed against an increased risk of aseptic loosening when compared to cementless CMDF stems.